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  2. Facts about mobile communications and health /
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How mobile telephony works

What happens when you make a mobile phone call?

When you make a mobile phone call, your phone makes radio contact with the mobile phone network, sending radio signals to the closest radio base station, which, in turn, sends the call on to a mobile switch. If you are calling someone who uses an ordinary wired telephone, the mobile switch sends the call to the fixed network. If you are calling another mobile phone user, the switch routes the call to another base station, whose antenna sends the call as radio signals to the other user's mobile phone. Calls are two-way, so in other words, mobile phones and their base stations both send and receive radio signals.

Since mobile telephones have a limited range, you can make calls only if there is a base station within range. That is why base stations are located at regular intervals according to a fixed pattern, just as street lamps are evenly spaced to light the way along a road. Each base station serves a given geographical area called a cell. When you move from one cell to another - driving along a highway, for instance - the base station serving the new cell automatically picks up the signals from your call.